Protein S is a vitamin K-dependent plasma protein that inhibits blood clotting by serving as a cofactor for activated protein C. Protein S exists in 2 forms in plasma: the free, functionally active form and the inactive form complexed with C4b-binding protein (Dahlback and Stenflo, 1981). Just as deficiency of protein C causes thrombotic disease, partial protein S deficiency is associated with severe recurrent venous thrombosis.
General function
Comment
Vitamin-K-dependent protein S is an anticoagulant plasma protein which functions as cofactor to activated protein C (APC) in the degradation of coagulation factors Va and VIIIa. In addition, it interacts with C4b-binding protein (C4BP), a regulator of the complement system. In human plasma, around 40% of protein S circulates as a free protein, while the remaining 60% forms a noncovalent 1:1 stoichiometric complex with the beta-chain of the complement C4b-binding protein (C4BPB) (Dahlback, 1991). This interaction is of high affinity and abolishes the anticoagulant properties of protein S.
Cellular localization
Secreted
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Ovarian function
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Expression regulated by
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thrombin
Ovarian localization
Stromal cells
Comment
Northern blotting demonstrated protein S mRNA not only in liver but also in reproductive organs (testis, ovary and uterus), in lung and brain (He et al., 1993). He et al. (1995) reported that protein S mRNA was present in the interstitial cells of the ovary. Immunohistochemistry with monoclonal antibodies yielded a staining pattern that correlated well with results of in situ hybridization.
. Strong staining reac-
tions were observed in the interstitial cells of ovary (Figure 5). These
cells were mostly distributed in the medulla and around the ovum
follicles, with the strongest staining in the hilar region of ovary.
Germinal epithelial cells, cells in the tunica albuginea, and ova
of different stages were unstained.
Follicle stages
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Phenotypes
Mutations
1 mutations
Species: human
Mutation name: None
type: naturally occurring fertility: fertile Comment:Mannucci et al. (1989) found a dysfunctional protein S, present in plasma in normal amounts and with normal proportions of the free and complexed forms, in a woman who developed deep vein thrombosis while taking oral contraceptives. Five other family members in the same and the preceding generation had the same laboratory abnormality but were asymptomatic.